Percussion tool



June 6, 1939. R. J. KILLGORE 2,161,062

PERCUSSION TOOL Filed March 24, 1954 [/v m TOR A 7'7'ORNEY.

Rosa/QT (1 K/LLGORE Patented June 6, 1935.

UNITED STATES ATEN OFFICE 3 Claims.

My invention relates to a tool of percussion type adapted to be drivenagainst or into the material on which the tool is caused to operate.

My invention is of especial utility in the break- 5 ing up of materials,such asconcrete, brickwork, rock, etc. The razing of concrete structuresand the breaking up of concrete pavements for the purpose of cuttingditches or removing or replacing a road surface is generallyaccomplished by use of a sharp pointed steel bit or gad operated in anair hammer. Due to the very abrasive character of the materials operatedupon, it is found that tools used for this purpose lose their cuttingpoints very quickly and must be frequently resharpened. My inventionprovides a tool adapted for the very severe service of breaking upconcrete andother materials of a similar character, which tool isself-sharpening. In addition to being self-sharpening, this tool isotherwise as strong and durable as the steel, gads now employed.

It is an object of the invention to provide a percussion tool of theabove character comprising abar or body of tough metal which will standup for a maximum period of time against the severe crystallizationinfluences encountered in air hammer operation, having an insert ofextremely hard steel set into the pointed cutting end thereof in such amanner that the insert, whichd'ue to its 30 great hardness is somewhatbrittle, will not break in ordinary usageof the tool but will preserve asharp point for the tool owing to the fact that the surrounding metal inwhich the insert is held, although being of larger volume, wears faster35 than the point of the insert and thereby preserves a continuouslysharp cutting point for the tool.

It is an object of theinvention to provide a simple manner and means forholding the hard insert in the softer tough bar in such a manner thatthe insert will not break up due to the stresses applied thereto.

A further object of the inventionis to provide in a tool of the abovecharacter a tough metal body of characteristic form surrounding the in-45 sert so as to firmly secure the insert in such a manner that forcesreceived by the point of the insert are transmitted from the side wallsof the insert to the supporting body of metal instead of through the endof the insert to the supporting 50 body of metal, thereby producing adistribution of forces which will prevent breakage of the insert due toits severe use.

Further objects and advantages of the invenus ing part of thespecification.

Referring to the drawing, which is for illustrative purposes only,

Fig. 1 is a view showing a preferred form of my invention and a mannerof its use. I

Fig. 2 is a perspective view of the percussion 5 tool.

Fig. 3 is an enlarged sectional view of the point of the tool.

Fig. 4 is a view looking at' the pointed end of the tool. 10

In Fig 1 I show my percussion tool or gad fitted into an air hammer |2so that it may be manipulated by a workman l3 against a body of materialM, such, for example, as concrete, which is to be broken up so that itmay be removed. it

' 'fect. The forward end of the bar l5 has a longitudinal opening 2|leading inwardly therefrom, this opening being tapered inwardly as shownand receiving therein a hard metal insert 22, the end of which issharpened or pointed; as shown at 23, to cooperate with the end of thebar in forming the cutting point of the percussion tool.

The opening 2| is made of greater length than the insert 22, and theinsert 22 is tapered to correspond to the taper of the opening 2| sothat the insert 22 will not bottom in the opening or hole 2| but leavesa space 24 between the inner end 25 thereof and the bottom 26 of theopening 2| which is rounded so that no sharp corners exist from which acrack may readily start in the metal forming the bar I5. v

In the preferred form of my invention the re- 40 action forces exertedagainst the tip or point. 23 of the insert 22 are transmitted throughthe tapered side wall thereof to the tapered wall of the opening 2|instead of directly axially through the insert 22 to the bottom of theopening 2|. In

this construction the forces are distributed through a comparativelylarge external area of the insert 22, with the result that the verysevere impact which must be transmitted through the insert 22 does notresult in the insert being broken, even though it may be of relativelybrittle material.

The bar l5 is-made from a metal which has toughness as its outstandingcharacteristic. It is found that gads are subject to breakage in the 5shank portion thereof due to crystallization of the metal; therefore,the metal employed must be extremely tough. I find that satisfactoryresults can be obtained where the bar I5 is made from chrome-tungstensteel or similar alloys, including molybdenum and other of the efiectivehardening elements. The insert 22 is made of a metal having extremehardness as its principal characteristic. Accordingly, such metal isquite brittle and could not be employed throughout the entire percussiontool or gad due to its brittleness. In my invention, however, the hardinsert 22 is supported, and the stresses are distributed therein,in'such a manner that breakage thereof does not ordinarily occur. I findthat one metal suitable for use in the insert 22 is high speed toolsteel, of which there are several kinds, such as Panther, Rex, etc. Inorder to provide a control of the wear at the cutting end of the toolI5, the hardness of the bar [5 and the hardness of the insert 22 areproportioned with this end in view. I find that good results areobtainable where the bar It: has a hardness of 40 Rockwell and theinsert 22 has a hardness of 60 Rockwell. It is evident, however, thatthese values may be materially changed in the practice of the invention.

The taper of the insert 22 and the opening 2! is such that the insert 22will not be forced into the opening in the use of the tool. The degreeof taper accordingly is determined from the characteristics of themetals employed in the bar It: and in the insert 22. For example, as thestrength of the metal surrounding the opening 2i increases, the taper ofthe opening may be decreased, but should the bar l5 be made of a metalwhich, although very durable, is of decreased tensile strength, thetaper of the opening 2| and of theinsert 22 will be proportionatelyincreased. A simple manner of placing the insert 22 in operativeposition consists in heating the walls of the bar 35 surrounding theopeningZI so as to increase the diameter of the opening and then forcethe insert 22 into the opening while it is thus enlarged, the metalwalls surrounding the opening 2i shrinking down upon and firmly grippingthe insert 22 when they are returned to normal temperature. 1

An additional feature of the invention resides in the formation of apoint on the end of the bar l5 which will be of such form that amplemetal will be provided for support of the hard metal insert.Accordingly, the wall or walls 20 of the point l8 extend through arelatively small angle of taper 21 to a plane A--A near the extreme endof the tool, whereupon the taper is abruptly increased throughout theshort area 28 in the formation of the actual point of the tool. In thismanner the metal at 30 is maintained amply thick for the support of theinsert 22.

Although I have herein shown and described my invention in simple andpractical form, it is recognized that certain parts or elements thereofare representative of other parts, elements, or mechanisms which may beused in substantially the same manner to accomplish substantially thesame results; therefore, it is to be understood that the invention isnot to be limited to the details disclosed herein but is to be accordedthe full scope of the following claims.

I claim as my invention:

1. A cutting tool of the character described for use in cutting hardmaterials, comprising: a body of relatively tough metal having a taperedopening extending inwardly from the cutting portion thereof, the innerend of the wall forming said opening being gradually reduced to form abottom for said opening without the formation of an abrupt shoulder; anda tapered insert of hard metal in said opening in such position that theinner end of said insert will be spaced from the bottom of said opening,the walls of said body around said opening being so formed as to holdsaid insert in radial compression.

2. A cutting tool of the character described for use in cutting hardmaterials, comprising: a body of relatively tough metal having anopening extending inwardly from the cutting portion thereof, the innerend of the Wall forming said opening being gradually reduced to form abottom for said opening without the formation of an abrupt shoulder; andan insert of hard metal in said opening in such position that the innerend of said insert will be spaced from the bottom of said opening, thewallsof said body around said opening being so formed as to hold saidinsert in radial compression with sufficient force to substantiallyprevent shattering of said insert.

' 3. A digging tool having a tapered metallic point and being formedwith a longitudinally extending tapered bore disposed centrally thereofwith its outer larger diameter agreeing substantially with the diameterof the outer end of the body portion, a tapered steel insert of greaterhardness than that of the body portion, the largest diameter of saidinsert substantially agreeing with the diameter of the end of the point,the body portion of the insertfitting into the tapered bore and being ofa length substantially less than the length of the bore and having anouter point projecting beyond the end of the pointed body portion.

ROBERT J. KILLGORE.

